1. Field of the Invention
This invention relates to a metal hydride container comprising a heat pipe of annular cross section and a metal hydride filling the central cavity of the heat pipe, and to a heat storage system comprising an insulating body having at least one such metal hydride container inserted fast therein, a heat exchanger, a hydrogen gas distributor, and a hydrogen storage tank.
2. Description of the Prior Art
The technique of heat storage using a metal hydride is attracting attention as a novel method of heat storage which is capable of utilizing heat (such as solar heat or plant's waste heat) for a long time. This method features (1) capability of prolonged heat storage, (2) quick reaction of metal and hydrogen, (3) easy control of the reaction solely by regulation of gas flow, and (4) large amount of heat storage per unit volume, for example.
Yet, the method has problems: (1) As the cycle of absorption and desorption of hydrogen is repeated, the metal hydride gradually undergoes comminution and loss of volume. (2) Since the metal hydride itself has low thermal conductivity, it suffers from inferior heat transfer (transfer of heat of reaction). As a measure to overcome these problems, it is advantageous to adopt the multi-tube heat exchanger method which uses as many separate containers for the metal hydride as possible and which, therefore, furthers the capacity of the metal hydride for contact with the heat transfer tubes even when the metal hydride suffers from loss of volume (First World Hydrogen Energy Conference, Mar. 1-3, 1976, Miami Beach, Fla., U.S.A., Conference Proceedings Volume III, 7C-22). And as a measure to eliminate the difficulty of (2), the aforementioned multi-tube heat exchanger method proves advantageous and the incorporation of a thermally conductive powder (such as, for example, copper, silver, or aluminum) in the metal hydride is effective.
The heat storage system using a metal hydride has another disadvantage that the heat of reaction of the metal hydride is wasted in the form of sensible heat to the container. Either the aforementioned multi-tube heat exchanger method or the method which simply confines the metal hydride in a pressure vessel so as to recover the heat of reaction directly [by keeping a copper coil within the vessel thereby recovering the heat of reaction with a heat medium such as water circulated through the copper coil; Philips Research Reports, Supplement, No. 1 (1976), pages 71-73 ] or indirectly (by having a heat transfer pipe such as a heat pipe inserted in advance in the vessel thereby recovering the heat of reaction via a heat exchanger provided at the exposed end of the heat pipe; Japanese Laid-Open Patent Application No. 53390/1980) does not prove satisfactory for the purpose of reducing the loss of sensible heat.
This invention has been perfected for the purpose of solving the various problems described above and provides a novel metal hydride container possessed of excellent properties and a heat storage system using the metal hydride container.